Friday, July 6, 2012

Albedo change in the Arctic

Albedo change: Snow cover on the ice reflects between 80% and 90% of sunlight, while the dark ocean without ice cover reflects only 7% of the light, explains Stephen Hudson of the Norwegian Polar Institute. As the sea ice cover decreases, less solar radiation is reflected away from the surface of the Earth in a feedback effect that causes more heat to be absorbed and consequently melting to occur faster still.

As shown on the image below, by Wipneus and earlier published at the Arctic Sea Ice Blog, sea ice volume is on track to reach a minimum of 3000 cubic kilometers this summer.

The recent sea ice volume is in line with the exponential trend calculated by Wipneus that is pointing at zero ice volume around 2015 (image below).

As described earlier, I believe that a trendline pointing at 2014 fits the data best (image left).

While some ice may persist close to Greenland for a few years more, this applies only to a relatively small area; this does not revert the curve downwards as it applies to the remainder of the Arctic Ocean. Moreover, there is robust evidence that global warming will increase the intensity of extreme weather events, so more heavy winds and more intense storms can be expected to increasingly break up the remaining sea ice in future, driving the smaller parts out of the Arctic Ocean more easily.

Apart from the albedo change that comes with this loss of sea ice, there's also the loss of snow cover on land. Snow cover over Northern Hemisphere lands retreated rapidly in May and June, leaving the Arctic Ocean coastline nearly snow free, says the National Snow & Ice Data Center (NSIDC), adding that this rapid and early retreat of snow cover exposes large, darker underlying surfaces to the sun early in the season, fostering higher air temperatures and warmer soils.

The joint impact of loss of sea ice and loss of snow cover on land will make a huge difference; much more sunlight is now absorbed, instead of reflected back as was previously the case.

Below are calculations by Professor Peter Wadhams, University of Cambridge. Earth has a total surface area of 510,072,000 square km (196,888,000 square miles), as the table below shows, byMichael Pidwirny, or about 510 million square km.

Surface

Percent of Earth’s Total Surface Area

Area Square Kilometers

Area Square Miles

Earth’s Surface Area Covered by Land

29.2%

148,940,000

57,491,000

Earth’s Surface Area Covered by Water

70.8%

361,132,000

139,397,000

Pacific Ocean

30.5%

155,557,000

60,045,000

Atlantic Ocean

20.8%

76,762,000

29,630,000

Indian Ocean

14.4%

68,556,000

26,463,000

Southern Ocean

4.0%

20,327,000

7,846,000

Arctic Ocean

2.8%

14,056,000

5,426,000

Professor Wadhams estimates the present summer area of sea ice at 4 million square km, with a summer albedo of about 0.60 (surface covered with melt pools). When the sea ice disappears, this is replaced by open water with an albedo of about 0.10. This will reduce the albedo of a fraction 4/510 of the earth's surface by an amount 0.50. The average albedo of Earth at present is about 0.29. So, the disappearance of summer ice will reduce the global average albedo by 0.0039, which is about 1.35% relative to its present value.

As NASA describes, a drop of as little as 0.01 in Earth’s albedo would have a major warming influence on climate—roughly equal to the effect of doubling the amount of carbon dioxide in the atmosphere, which would cause Earth to retain an additional 3.4 watts of energy for every square meter of surface area.

Based on these figures, Professor Wadhams concludes that a drop in albedo of 0.0039 is equivalent to a 1.3 W/sq m increase in radiative forcing globally.

The albedo change resulting from the snowline retreat on land is similarly large, so the combined impact could be well over 2 W/sq m. By comparison, this would more than double the net 1.6 W/sq m radiative forcing resulting from the emissions caused by all people of the world (see IPCC image below). Professor Wadhams adds: "Remember that this is going to happen in only about 3 years if the predictions of alarmist glaciologists like myself are correct".

8 comments:

I think would be more accurate at the top to say that sea ice volume (rather than sea ice volume loss) is on track to reach a minimum of 3,000 cubic kilometers. Otherwise, very informative post, thanks.

With all respect to prof. Wadhams, i feel that his calculations about albedo change are to be corrected, by adding into the picture the simple fact: unlike majority of Earth surface, Arctic experience polay days and nights, - periods when Sun shines 24/7 and 0/0, correspondedly. Since we talk here about loss of ~4^6km^2 of _summer_ ice in last 3 decades or so, - and expected loss of 4 more in a few years, - it is required to (very roughly) double albedo change, if we are to apply changes to Earth's total albedo.

Additionally, what use we have from winter ice in Arctic in terms of good albedo, if there is ZERO sunlight reaching Arctic surface in winter?

From those points, purely amateruly, without considering autums/springs in Arctic (i mean times of the year when Sun is above the horizon for more than 0, but less than 24 hours a day), and without considering most likely mighty effective albedo changes via dissipation of sunlight in the athmosphere for times/places in Arctic when/where Sun is only few degrees above horizon (<3° or so), and adding snow loss of ~4^6km^2 mentioned in the main post, i'd say that

combined impact could be more than +4W/m^2.

If you have any chance to let prof. Wadhams know about this simple yet quite (imho) realistical correction of mine, then please do so, Sam. He'll probably want to know.

Yes, there are many local factors that could be included in the formula, such the solar elevation angle, the fact that days are longer in the Arctic summer, presence of ice, of clouds, changes to the polar vortex and jet stream, storms, currents, etc.

Indeed, apart from calculating the global impact of albedo change, it's important to look at local impact. In the Arctic, the impact will be greater in summer. There have been studies into this, such as the excellent study by Flanner et al, which is discussed in section 6 (RF) of the Arctic sea ice page. As the image shows, at some locations the difference can be more than 30 W per square meter.

Sam, thanks for links alot, i'll be sure to learn as much as i can from those.

Also.

It was long-time thought of mine, by the way, that relatively sharp average angle at which Sun is shining over Arctic should be one of factors responsbile for accelerated arctic warming in present conditions. I mean the fact that Sun at north/south poles never gets higher than 23° above horizon, yet shines for several months without going below horizon - polar day. Similar picture is for both polar regions, with more and more "normal daily" behaviour we all used to in moderate/tropic places the further away it is from the poles. Obviously, on average "per year", in the Arctic/Antarctic, sunlight goes times longer distance through dense layers of the athmosphere before it can reach the surface - times longer in polar regions in compare to tropics, for example, where majority of the time Sun shines - it shines from much higher point than just 23° above horizon. With unnaturally high GHG concentrations we have today (and will surely have for at very least few decades ahead), times longer distance to travel through dense part of the athmosphere causes times higher chances for any given photon to be "caught" by a molecule of GHG gas and thus re-emitted as lower wave energy - heat (ifrared radiation). I am pretty sure that this is one of factors to times-faster-than-world-average warming in Arctic, but i am not sure about how significant in compare to other factors this one is. Bad thing, though, is that we can do absolutely nothing to remove this one, and another bad thing is that with time and with presense of long-lived GHGs such as CO2 and some CFCs, net effect from this one will accumulate, melting more and more ice until there is simply nothing left summer-time. CO2/CFCs have centuries to pile up that ambient heat, and somehow i think that lots of models/papers do not account for this simple geometry of Arctic regions.

Those of photons which reach Arctic surface without being transformed into IR (heat), - have a chance to be reflected (albedo). If they are reflected, then often they get out in same sharp (to surface) angle they came in (if reflected from horizontal surface, which is the case quite often). Thus, one more "long way out" is to be taken by such photons, and of course, on this way - out of athmosphere - they have same, times increased in compare to tropics, chances to be "caught" by GHGs, and thus be re-emitted as heat.

Which has somewhat reducing effect on estimated above "combined impact" of albedo change: before we lost those 4^6km^2 of snow and 4 of ice, those surfaces were reflecting ~6 times more light into outer space, true - but, not all of that reflected light actually made out, some was consumed by GHGs, and geometry i talk above increases that fraction in compare to any consideration which does not take said geometry into account, and substantially so.

Dropping albedo from 0.6 to 0.1 means 6 times less photons are reflected, thus 6 time less photons are caught by GHGs in dense layers of Arctic athmosphere on their way out. This mechanism alone will likely change athmopheric processes in Arctic (summertime that is), by increasing the gap between average temperature of near-surface layers and near-tropopause layers of the athmosphere in Arctic - i _guess_, that is. Perhaps said gap would increase only by a small fraction of a degree (talking averages of course)? Or tiny fraction? Or may be few degrees? No idea about scale of this. Yet in any case, since colder things tend to do down and warmer things tend to go up (convedction), this would lead to faster wind speed and more/larger cyclones - either significantly or not, i don't know. If significantly, though, then consequences to remaining ice would be massively destructive, i recon.

Yes, the sun's angle is a factor, but only one out of many. Length of day is another factor. In June, daily average insolation in the Arctic is higher than anywhere else on Earth. Yes, much of the heat that now still is reflected or goes into melting the ice could translate into storms in the Arctic, which is part of many of the feedbacks pictured in the Diagram of Doom.

There are many factors that determine how much sunlight is reflected back into space. Much depends on the sun's angle, at a 50 degree angle almost all sunlight can be absorbed, while the higher reflectivities only occur at angles close to 90 degree when the sunlight is a lot stronger as it has to travel through less atmosphere. In open water, more stroms can be expected, and waves make that more sunlight is absorbed, while clouds constitute another factor. Perhaps it's technically more accurate to say that snow cover on the ice reflects as much as 90% of sunlight, while the dark ocean without ice cover reflects as little as 7% of the light, but the post highlights the principle that as the sea ice retreats, more heat will be absorbed by the water. Similarly, as permafrost retreats on land, more heat will be absobed.

Videos

Global temperatures are rising fast. In the Arctic, temperatures are rising even faster (interactive charts below and right). For 2010 and 2011, NASA recorded anomalies of over 2°C at higher latitudes (64N to 90N), with anomalies of over 3°C at latitudes 79N and 81N in 2010.

For November 2010, anomalies of 12.5°C were recorded at latitude 71N, longitude -79 (Baffin Island, Canada). At specific moments in time and at specific locations, anomalies can be even more striking. As an example, on January 6, 2011, temperature in Coral Harbour, located at the northwest corner of Hudson Bay in the province of Nunavut, Canada, was 30°C (54°F) above average.